We all should know that minor scratches on the front of lenses generally
have no noticeable effect on image quality. Really big or sharp ones
need to be blacked out to avois added flare and contrast reduction, but
otherwise they are way out of focus and don't show up. The same thing
applies to filters. The more important question is what happens to light
when is passes through them. The problem is that the naked eye can't
answer that question. See Gary's tests of the '50mm f/1.4 Zuiko
(multi-coated) OM-2000 with mirror and diaphram prefire; lens with
>1,100,000' with and without bad filter
<http://members.aol.com/olympusom/lenstests/default.htm>I don't think
there is any inherent theoretical reason why plastic would be worse than
glass. I think one can assume there is nothing much wrong with Cokin
filters simply from their longevity as a product.
Moose
John Hudson wrote:
Are there any cokin filter users, or others, on the list who can opine
as to the quality of cokin filters and any resulting image degradation
as compared to using high quality optical glass filters? Just off the
top of my head I have to think that cokin's plastic filters result in
greater image degredation than high quality B+W and Heliopan filters
for example and also are more prone to scratching than glass filters.
John Hudson
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